<template>
    <ul class="list">
        <li class="item"
            v-for="item of letters"
            :key="item"
            @touchstart.prevent="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
            @click="handleLetterClick"
            :ref="item"
        >
            {{item}}
        </li>
    </ul>
</template>

<script>
    export default {
        name: "Alphabet",
        props: {
            cities:[Array,Object]
        },
        computed: {
            letters(){
                let letters = [];
                for(let i in this.cities){
                    letters.push(i);
                }
                return letters;
            }
        },
        data(){
            return {
                touchStatus: false,
                startY: 0,
                timer: null,
            }
        },
        updated (){
            this.startY = this.$refs['A'][0].offsetTop;
        },
        methods: {
            handleLetterClick(e){
                this.$emit('change',e.target.innerText);
            },
            handleTouchStart(){
                this.touchStatus = true;
            },
            handleTouchMove(e){
                if(this.touchStatus){
                    if(this.timer){
                        clearTimeout(this.timer)
                    }
                    this.timer = setTimeout(() => {
                        let touchY = e.touches[0].clientY - 79;     //手指到顶部的距离
                        let index = Math.floor((touchY - this.startY) / 20 );//20为每个字母的高度，判断出是第几个字母
                        if(index >= 0 && index <= this.letters.length){
                            this.$emit('change',this.letters[index]);
                        }
                    },20);
                }
            },
            handleTouchEnd(){
                this.touchStatus = false;
            },
        }
    }
</script>

<style lang="stylus" scoped>
    @import "~@/assets/vavibles.styl"
    .list
        position absolute
        display flex
        flex-direction column
        justify-content center
        top 1.58rem
        bottom 0
        right 0
        width .4rem
        .item
            text-align center
            line-height .4rem
            color $bgColor
</style>
